1. Field of the Invention
The present invention relates to a semiconductor device and forming method thereof. More particularly, the present invention relates to a capacitance dielectric layer, a forming method thereof and a capacitor.
2. Description of the Related Art
In recent years, with the rapid development of integrated circuit manufacturing industry, the miniaturization of devices and the increase in the level of integration continue unabated. As a result, the design of circuit devices is advancing toward ever-decreasing dimensions.
FIG. 1 is a schematic cross-sectional view of a conventional capacitor. In general, a capacitor 100 mainly comprises a bottom electrode plate 105, a capacitance dielectric layer 110 and a top electrode plate 120. The top electrode plate 120 and the bottom electrode plate 105 are mostly fabricated using polysilicon. The capacitance dielectric layer 110 is normally a three-layered structure comprising a silicon oxide layer 112, a silicon nitride layer 114 and another silicon oxide layer 116. This kind of dielectric layer structure is often referred to as an oxide/nitride/oxide (ONO) composite structure.
It should be noted that with the continuous reduction in device dimension, the capacitor structure inside some mixed mode devices or radio frequency (RF) devices may encounter the problem of not having enough per unit capacitance. To resolve this problem, it is customary to reduce the thickness of the capacitance dielectric layer so that the per-unit capacitance of the capacitor can increase.
However, as shown in FIG. 1, the thickness of the capacitance dielectric layer 110 is mainly contributed by the silicon nitride layer 114 disposed in the middle of the capacitor 100. At present, most capacitance dielectric layer is formed in a single one-time deposition process. If the thickness of the capacitance dielectric layer is directly reduced using the same process, significant number of defects 130 such as seams or pinholes can easily form in the capacitance dielectric layer, particularly, the silicon nitride portion. These defects will serve as pathways for leakage currents so that the leakage current will increase and the breakdown voltage of the capacitor will reduce. Ultimately, data may be lost and the processing reliability and yield may be affected.